Magnesium glycinate vs citrate vs oxide vs threonate
According to the NIH Office of Dietary Supplements, forms of magnesium that dissolve well — including citrate — are absorbed more completely than magnesium oxide in small studies. Glycinate is widely marketed as gentle and well absorbed, but comparative human evidence is thinner; threonate has a small number of manufacturer-linked trials on cognition. Whatever the form, labels list elemental magnesium, and the adult upper limit for magnesium from supplements is 350 mg a day.
This article answers one question. For what Magnesium is, where it comes from and its other uses, see the Magnesium ingredient guide.
Key findings
- Citrate, aspartate, lactate and chloride were absorbed more completely than oxide and sulfate in small studies (NIH ODS).
- Labels state elemental magnesium, not the weight of the whole compound.
- Adult upper limit from supplements: 350 mg a day; higher amounts commonly cause diarrhoea.
- Threonate evidence for cognition comes mainly from one small developer-linked trial and newer industry-funded work.
How the forms compare
| Form | Absorption evidence | Typical use context | Notes |
|---|---|---|---|
| Magnesium oxide | Less completely absorbed than more soluble forms in small studies (ODS) | Low-cost supplements, laxatives, antacids | High magnesium content per tablet but lower absorption |
| Magnesium citrate | More completely absorbed than oxide in small studies (ODS) | General supplementation; laxative at higher doses | Can loosen stools |
| Magnesium glycinate (bisglycinate) | Not among the forms ODS lists from small comparison studies; direct comparative data are limited | Marketed for sleep and tolerability | Evidence for superiority is mostly marketing and indirect |
| Magnesium L-threonate | Developed to raise brain magnesium in animal work | Cognition and sleep marketing | Human trials few and industry-linked |
What human research shows
The NIH ODS magnesium fact sheet states that magnesium forms that dissolve well in liquid are absorbed more completely, and that small studies found aspartate, citrate, lactate and chloride forms more bioavailable than oxide and sulfate. For threonate, a 12-week randomised, double-blind trial in adults aged 50–70 with cognitive complaints, sleep problems and anxiety reported improved overall cognitive scores versus placebo; effects on sleep and anxiety could not be determined because of strong placebo responses (Liu et al., 2016). The corresponding author was affiliated with the company developing the compound. A 2026 six-week trial of a branded threonate by an industry-funded research group has also been published (Lopresti & Smith, Front Nutr).
Evidence table
| Study or source | Population | What was tested | Main result | Limitations |
|---|---|---|---|---|
| NIH ODS magnesium fact sheet | Summary of small absorption studies | Different magnesium salts | Aspartate, citrate, lactate, chloride more bioavailable than oxide and sulfate | Small, short studies |
| Liu et al., 2016 | Adults 50–70 with cognitive complaints | Magnesium L-threonate (MMFS-01) vs placebo, 12 weeks | Improved composite cognitive score; sleep/anxiety effects undetermined | Single site; developer-linked |
| Lopresti & Smith, 2026 | Adults | Branded magnesium L-threonate vs placebo, 6 weeks | Assessed cognition and sleep | Industry-linked research group |
Doses: what each number means
| Amount | What kind of figure it is | Context |
|---|---|---|
| 350 mg/day from supplements | Upper limit | Adult tolerable upper intake level for supplemental magnesium |
| Elemental magnesium on label | Label rule | Supplement Facts panels declare elemental magnesium, not compound weight (ODS) |
| Compound amounts (e.g. 2,000 mg threonate) | Commercial dose | Refers to the whole compound; elemental magnesium is much lower |
A dose used in a study describes what researchers gave participants. It is not a personal recommendation, and it does not mean a lower or higher amount is safe or effective for you.
Safety
- Supplemental magnesium above the upper limit commonly causes diarrhoea, nausea and cramping.
- People with reduced kidney function are at risk of magnesium build-up and should use supplements only with medical advice.
- Magnesium can reduce absorption of some antibiotics and osteoporosis medicines when taken at the same time; separate doses and ask a pharmacist (ODS).
Limitations
- Absorption studies are small and short.
- Better absorption does not automatically mean better clinical outcomes.
- Glycinate and threonate claims rely more on marketing than on comparative trials.
Label checks
- Elemental magnesium per serving (the Supplement Facts figure).
- Form named on the label.
- Total supplemental magnesium across products versus 350 mg a day.
- For threonate, whether amounts refer to the compound or elemental magnesium.
Related: magnesium guide · glycinate · citrate · oxide · L-threonate · does magnesium help sleep
Frequently asked questions
Which magnesium form is best absorbed?
Small studies summarised by NIH ODS found citrate, aspartate, lactate and chloride better absorbed than oxide and sulfate.
Is magnesium glycinate better than citrate?
Direct comparative evidence is limited; glycinate is often preferred for tolerability, but superiority is not well established.
Does magnesium threonate improve memory?
A small 12-week developer-linked trial reported improved cognitive scores; independent confirmation is limited.
What is the upper limit for magnesium supplements?
350 mg a day from supplements for adults.
Why does magnesium oxide cause diarrhoea?
Unabsorbed magnesium draws water into the bowel, which is why it is used as a laxative.
References
- NIH ODS magnesium fact sheet.
- Liu G, et al. Efficacy and safety of MMFS-01, a synapse density enhancer, for treating cognitive impairment in older adults. J Alzheimers Dis. 2016;49(4):971–990. PMID 26519439
- Lopresti AL, Smith SJ. The effects of magnesium L-threonate (Magtein) on cognitive performance and sleep quality in adults. Front Nutr. 2026. PMC12832366